Please help me out. 1969 100w build

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neikeel
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Re: Please help me out. 1969 100w build

Post by neikeel » Tue May 01, 2018 10:31 am

As per my short post above (sorry - busy!) the heater chain is not complete beteeen V2 and V3, I see poor solder joints on the red heater wires of V2, I suspect that is the issue.

I cannot see any other major issues.

I agree with Tazin that it might be prudent to reflow some of the solder joints in a few places:

Where the V3 plate resistors (100k/82k) meet

The green wire on the board on the 220k grid leak (aka bias splitter)

Where V2a cathode resistor (820R/0.68uF) and cap go to yellow turret - looks grey and maybe a cold joint.

Take a nicely warmed up iron in good light with glasses and touch up any joint that is dull or where the lug is not full, and dab the solder to flow into the joint etc.

Please post back when you have done these things 8)
Neil

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Thu May 03, 2018 3:59 pm

neikeel wrote:
Tue May 01, 2018 10:31 am
As per my short post above (sorry - busy!) the heater chain is not complete beteeen V2 and V3, I see poor solder joints on the red heater wires of V2, I suspect that is the issue.

I cannot see any other major issues.

I agree with Tazin that it might be prudent to reflow some of the solder joints in a few places:

Where the V3 plate resistors (100k/82k) meet

The green wire on the board on the 220k grid leak (aka bias splitter)

Where V2a cathode resistor (820R/0.68uF) and cap go to yellow turret - looks grey and maybe a cold joint.

Take a nicely warmed up iron in good light with glasses and touch up any joint that is dull or where the lug is not full, and dab the solder to flow into the joint etc.

Please post back when you have done these things 8)
Thank you Neikeel & Tazin. I've gone through all solder joints as you suggested. The 2 yellow wires to the 8K2 2W resistor are from V4 pin 6 and the F3 capacitor, depicted in assembly instructions here, step 13
http://valvestorm.com/sites/default/fil ... MP_KIT.pdf

I'm using a modified grounding scheme found here:
https://drive.google.com/drive/folders/ ... EFwZHpXN3M (version #6). I intend on adding the PPMIV when the amp is working.

New link to see updated photos (conflicting photos removed), voltage chart (1st photo) still showing odd numbers. https://www.flickr.com/gp/wedinbordeaux/3ta970

I appreciate your consideration!!

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neikeel
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Re: Please help me out. 1969 100w build

Post by neikeel » Thu May 03, 2018 4:11 pm

Have you reflowed the solder joints that I pointed out in my last thread?

Updated pics of the same?
Neil

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Re: Please help me out. 1969 100w build

Post by Tazin » Thu May 03, 2018 10:03 pm

The black heater wire on preamp socket V1 is a cold solder joint...Looks like there could be some contaminates on the tinned copper part of the wire. Carefully use a small razor blade or exacto knife and scrap the crud off before re-heating the solder joint.
Use your Multimeter to check the continuity for the heater wires from preamp socket V3 to V1.
Make sure the insulation on the Red link wire between filter cap F3 and F2(?) isn't causing a bad solder joint...Looks like it might have melted into the solder lug on the filter cap.
You've got three black ground wire located between Volume pot #1 & #2...Double check the middle black wire for a good connection.
Double check the connections on the preamp filter cap and make sure it's wire correctly. Additionly, check under the board for any foreign objects that don't belong...You may need to use a small dental mirror if the leads on the preamp filter capacitor are short.

Regarding the 10K & 8K2 B+ dropping resistors...I forgot that the Metroamp instuctions had them wired up this way. Marshall started this wiring scheme for the resistors on January 1, 1971 so prior amps (up til 1971) have it wired in the opposite direction.

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Sun May 06, 2018 6:30 pm

Thanks Tazin and Neil. Here's a link to current photos/voltage chart - readings are the same: https://www.flickr.com/gp/wedinbordeaux/p7k659

I went through every solder joint (with the exception of the cap under the board), cleaned up any dirt and made sure they were good. I've checked continuity between ALL tube sockets for heater continuity. The only thing I've not done is remove the turret board to see if there are any pinched wires - I have a dental mirror on order.

What do you think my next step should be?

Cheers!

Stephen

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Re: Please help me out. 1969 100w build

Post by Tazin » Sun May 06, 2018 8:42 pm

First off I have to say it weird to have both the Heater voltage and the H.T. (B+) voltage missing at the same time and only on the first two preamp tubes. Since the B+ voltage on the plates of the Phase Inverter (V3) seem normal I'd check the voltages at the two 10K/2w resistors (where the preamp filter wires connect to). Somehow the voltage is getting lost there. The voltage chart you posted is without tubes installed; correct?

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Mon May 07, 2018 12:28 am

Only the 12AX7's are installed.

would it be helpful for me to check voltage on ALL tube sockets and fill out the chart, entirely?

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neikeel
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Re: Please help me out. 1969 100w build

Post by neikeel » Mon May 07, 2018 6:30 am

no0sand1s wrote:
Mon May 07, 2018 12:28 am
Only the 12AX7's are installed.

would it be helpful for me to check voltage on ALL tube sockets and fill out the chart, entirely?
Yes, please do, this is quite funky given the numbers you have posted, but it cannot be that far off!
remind me which transformers you have used.
It does seem strange that the output tubes and PI have heater voltage. It is a chain, so by definition that chain is broken between v2 and v3 (maybe a broken wire if all your solder joints are correct)
same goes of the B+ rail - the power comes out of rectifier, into first filter cans and then to the choke/OT centre tap node, then from the other end of your choke to the screens, via the dropper resistors next to the bias circuit, then to the pi plates node and then to the mid board droppers. Might be worth lift in the board to make sure the solder joints and the ground connection quality is good on the preamp can.
Neil

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Re: Please help me out. 1969 100w build

Post by Tazin » Mon May 07, 2018 10:55 am

Yeah, we need a full voltage chart without any tubes installed. This way we can eliminate the tubes from possibly being the cause of the problem.

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Wed May 09, 2018 9:25 am

I had 2 realizations over the weekend. My post w/ only 2 sockets noted with odd voltages would lead everyone to believe the other sockets were fine. I've updated the list and checked both fuses (ok). I have Mercury Magnetics transformers/choke installed. Here's a new link to see the chart/photos. https://www.flickr.com/gp/wedinbordeaux/QW4752

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Re: Please help me out. 1969 100w build

Post by Tazin » Wed May 09, 2018 9:52 am

Oh wow!...All the voltages throughout the amp are screwed up with the possible exception of the bias voltage (although V4 does red 0vdc for bias voltage). I'll have to think about this while at work but my initial guess is something is wrong right around the rectification section or shortly after.

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Re: Please help me out. 1969 100w build

Post by Tazin » Wed May 09, 2018 12:54 pm

A quick thought while on lunch...I'd pull the H.T. Fuse and check the voltage there. Also make sure you have the Power Transformer grounds hooked up for the Bias supply & Heater Center Tap....Not sure which wire colors they are for the MP-100-460.

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Re: Please help me out. 1969 100w build

Post by neikeel » Wed May 09, 2018 1:44 pm

Ok so the 100-460 is:

Primary
orange is common to power switch which when on goes to the selector switch (or neutral if no voltage selector - is that black in US cords?). The red wire to the other half of the switch goes to one end of the mains fuse, the other end of which gets feed from power cord live (US = white?). Other power cord wire I presume is green which is ground?

Check you have 120vac across the mains switch

Secondaries
Blue/white and grey go to each half of the standby switch with the yellow centre tap to the junction of the mains cans (looks correct in pics)

check you have 350vac across the lugs of the standby switch

the feed to the cans comes to them via the red wire from the apex of the rectifier with another spur to the HT fuse which then via the fuse feeds the turret on the corner of the board.

check at this corner lug point (and on the fuse and red wire of mains filter cans) measure between ground and you should have about 460vdc.

Then follow the B+ line from that corner lug to the one where the choke feeds the screens (two yellow wires and choke wire) you will get a slight drop here - maybe 450vdc.

Chase along the droppers (to the lug where the 10k MO resistor hooks to the black wire and blue wire) you will get a 20-30v drop here.

Do these checks an post back
Neil

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Re: Please help me out. 1969 100w build

Post by Tazin » Wed May 09, 2018 3:43 pm

Neil outlined a very comprehensive troubleshooting guide for ya to follow...Hopefully this pinpoints to the problem.
In the USA White is neutral, Black is hot, and Green is ground.

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Wed May 09, 2018 7:41 pm

Tazin wrote:
Wed May 09, 2018 3:43 pm
Neil outlined a very comprehensive troubleshooting guide for ya to follow...Hopefully this pinpoints to the problem.
In the USA White is neutral, Black is hot, and Green is ground.
Thanks everyone! Wow - I appreciate your help. I'll let you know what I find when I get some free time.

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